This proposal has been designed to suit the training and career development objectives of Dr. Olga A. Cabello. The candidate has graduate training in Cardiovascular Physiology and Molecular Biophysics, and postdoctoral training in Cell Biology and Molecular Genetics. The proposed Career Development Plan (CDP) will provide her with additional skills in protein biochemistry, cell biological techniques and generation of transgenic animals. Dr. Cabello was recently appointed to a junior faculty position and her long term career goal is to establish an academic research program focused on molecular analysis of mammalian mitotic events and their role in genomic stability. Environment: The CDP is divided in two phases and is designed around the development of the Research Plan. Initially, the research activities will be conducted in the laboratory of Dr. H. Youssoufian, Department of Molecular and Human Genetics. Subsequently, the candidate will occupy her own research space in the Department of Cell Biology, under close supervision of Dr. B. R. Brinkley, ensuring a successful gradual transition to academic independence. All aspects of the five year CDP will be guided by an Advisory Committee. Research Plan: the mechanisms that adjoin newly replicated sister chromatid arms, and permit their precise separation at anaphase are incompletely understood, but may involve multiple processes including the degradation of adhesion proteins and the action of toppoisomerase II (topo II). She propose to analyze the human and mouse homologues of the recently describe Drosophila protein barren. Barren is required for chromatid arm separation possibly because of its modulatory action on topo II activity. They have partially characterized the gene encoding human barren (BRRN-1) and have identified other members of this putative gene family. They intend to test the hypothesis that barren function is conserved and that its activity in mammalian cells is similar to that observed in Drosophila. They will employ several strategies to gain insight into the function of BRRN-1 and its mechanism of action in human cells a) they will determine barren-1 expression and cell cycle-dependent subcellular localization, b) they will then evaluate the potential structural and functional interaction of barren-1 with topo II and mammalian homologues of SMC (structural maintenance of chromosomes) proteins. They will analyze the effect of simple and conditional targeted inactivation of mouse mbrrn1 in cultured ES cells. After successful production of these cell lines they will attempt the production of heterozygous mutant mice. The proposed studies should yield valuable information on the regulation of topoisomerase II and its participation in the anaphase process in mammalian cells. Also, they may provide new insights into human disorders of genomic stability. (End of Abstract)